It is known to provide a restraint system such as a seat belt system in a vehicle to restrain an occupant in a seat of the vehicle during a collision event. In some vehicles, the seat belt system may be a lap belt, a shoulder belt, or both. Typically, the lap belt and shoulder belt are connected together at one end. The seat belt system includes a tongue at the connected end. The seat belt system also includes a seat belt buckle connected at one end by seat belt webbing, a cable, or the like to vehicle structure. The buckle receives the tongue to be buckled together. When the buckle and tongue are buckled together, the seat belt system restrains movement of the occupant to help protect the occupant during a collision. Inflatable restraint systems, commonly referred to as “air bags”, are typically used in combination with seat belt systems to enhance occupant protection in a collision event.
It is desirable to configure smart inflatable restraint systems to determine what is occupying a seat of the vehicle in order to control deployment of inflatable restraints. Various ways to determine seat belt tension and determine if the seat belt is fastened have been proposed to provide information to the inflatable restraint system. However, the previously proposed solutions may be large and/or complicated and so are difficult to locate in the preferred but limited space around the seat frame. The previous solutions were also expensive. Previously proposed solutions that use a separate seat belt latch sensor and seat belt tension sensor presents additional difficulties for vehicle interior designers.